Recently, a rack mount method is the major trend in system composition, storage, and installation of information processing devices such as a server. The rack mount method is to mount devices with various functions on a rack, which fits a specific norm, by multiple layers. The system is able to freely select and place each device, to have excellent flexibility and expandability in system composition, and to reduce the area occupied by the whole system. Meanwhile, in relation to servers, a 19-inch rack specified by the International Electrical Commission (IEC) norm and the Electrical Industries Association (EIA) norm is the major trend. The 19-inch rack is specified to have a horizontal width of 451 mm of a supporter pillar for mounting devices and a height of 1 U (IEIA)=44.45 mm.
A rack mount server system is required to be able to cool down for effectively remove the heat generated in the server. In relation to the cooling technology of the rack mount server system, Japanese Publicized Patent No. 2004-246649 presents a cooling structure which cools with a liquid. Japanese Publicized Patent No. 2004-063755 provides a cooling structure which supplies cold air from an air-conditioning unit to an air inlet on the bottom of a rack, cools the devices in the rack with the cold air, and circulates the air by returning the heated air discharged from an air outlet on the top of the rack to the air-conditioning unit.
The rack mount server system having the above conventional rack cooling structure operates only a single cooling cycle. However, the cooling structure, in case of a disorder in the cooling device, has many issues such as a malfunction or maloperation of expensive computation equipment and an increase in power consumption. The conventional cooling structure is complex, making it difficult to manufacture and maintain it. Meanwhile, the rack mount server system must perform an efficient cooling in accordance with changes in temperatures. Here, an efficient cooling means optimize power consumption and cooling efficiency by considering the relations between the internal temperature of the server system and the external temperature. But, the conventional server system is not able to realize precise cooling in accordance with the internal temperature and the external temperature.